PHOENIX -- The results of a major new study on the benefits of mammograms run counter to what women have been told for years.

Published Tuesday in the British Medical Journal, the 25-year study looked at nearly 90,000 Canadian women between the ages of 40 and 50. Half of the women were randomly assigned to have mammograms. The other half received only physical breast exams and performed self exams.

Mammography screening, low-dose X-rays of the breast, is designed to help save lives through early detection of breast cancer. Mammograms are meant to find cancers that are too small to be felt.

Source: British Medical Journal

According to the study, however, mammograms offered no life-saving benefit. The death rate from breast cancer was statistically the same in both groups -- 500 women in the mammogram group and 505 in the breast-exam only group.

While the findings of the massive study probably will not have an immediate effect on mammography guidelines, they will fuel the debate between those who are staunch supporters of mammography as a detection tool and those who believe mammograms are at best worthless and at worst harmful.

Many breast cancer survivors say mammograms saved their lives.

While supporters of mammography argue that mammograms are one of the keys to early detection of breast cancer, there are those who say mammography results in over-diagnosis and over-treatment.

The analysis of roughly 30 years of data found that breast cancer screening has been spotting many early cancers that aren't life-threatening. The researchers estimate that more than a million women have been treated for cancers when they didn't need to be.

The Canadian study backed that up, finding that slightly more than 20 percent of the breast cancers found through mammography were not life-threatening.

The researchers on the newly published Canadian study say their results indicate that the role of mammography screening in breast cancer diagnosis needs to be reevaluated.

Dr. Angela DeRosa, a Scottsdale doctor who is a nationally known expert in women's health, generally recommends mammograms for her patients, but said she agrees with the new study for the most part. At the same time, she cautioned against rushing to judgment.

"As always, we need to be thoughtful in reactions," she said. "This [study] suggests that we may want to reevaluate mammograms and at least look at frequencies. Also, this stresses the importance of self breast exams and getting a yearly exam by your physician …."

DeRosa pointed out that doctors have other effective diagnostic tools, like the Provista blood test she offers at her offices, at their disposal.

When it comes to mammograms, there is no single black-or-white, yes-or-no answer.

"This is a highly loaded topic," DeRosa said. "We would be better spending resources on cardiovascular health but the breast topics are more emotional and sensational."

And not all of the experts are on the same page.

Guidelines created by the American Cancer Society suggest yearly mammograms starting at age 40. Those guidelines also recommend clinical breast exams every three years for women in their 20s and 30s and every year for women 40 and older.

Should ACS decide to change its guidelines, it would not happen until later this year.

While many doctors go by those standards, there are other recommendations.

"Having regular mammograms can lower the risk of dying from breast cancer," reads the Centers for Disease Control and Prevention's breast cancer Web page, which was last updated on Jan. 6. The CDC recommends a screening mammogram every two years for women 50-74.

Because the data and recommendations regarding the efficacy of mammograms often conflict, the best thing women can do is talk to their doctors to develop an individual course of action with which they are comfortable.

Breast cancer is the most common cancer in women -- not counting some kinds of skin cancer -- and one of the leading causes of cancer death among women, according to the CDC.